Dynamic optical networks are increasingly being introduced due to the availability of all optical switching technology such as wavelength selective switches embedded in (remotely) reconfigurable add drop multiplexers. A proposed control plane for optical networks is the generalized multi protocol label switching (GMPLS) protocol suite being developed by the internet engineering task force (IETF). The GMPLS application to optical networks is called wavelength switched optical network (WSON). The work of the IETF on WSON is detailed in its document “The framework for the control of wavelength switched optical networks (WSON) with impairments” (draft-ietf-ccamp-wson-impairments-02.txt). The IETF has also looked at proposing path computation element (PCE) technology to configure paths in optical networks, as summarized in its document “Framework for GMPLS and PCE control of wavelength switched optical networks” (draft-ietf-ccamp-rwa-wson-framework-06.txt).
The effect of physical constraints of the optical network, often referred to as impairments, impacts the routing of an optical signal across the network. The effect of impairments must be considered during the configuration of a path across an optical network to ensure that the optical signal transmitted across the path has sufficient quality to enable traffic carried by the signal to be detected at a receiver. The optical signal quality is usually quantified using a quality of transmission (QoT) parameter, which is strictly related to the bit error rate (BER) of the optical signal. The IETF documents referred to above propose estimating a QoT value for a path to be configured, the estimated QoT being based on information about the physical layer of the optical network and modeling of the physical layer performances. Using an estimated QoT value has the drawback that the QoT value is only an approximate value, and it is possible that the actual QoT of the path across the network will in fact not be acceptable, causing the path to fail. An alternative proposed in the IETF documents is to use a measured value of the QoT of the path to be configured. This can overcome the inaccuracy of the estimated QoT approach but the path can only be configured using a measured QoT value if the path has previously been configured. Traffic must have previously been successfully transmitted across the path, to allow the BER of the transmitted traffic signal to be measured and the QoT to be calculated.